Our body does not use the nitrogen we breathe–we
inhale it and exhale it. Being inert, nitrogen is unaltered
in the respiratory process and, for all practical purposes,
quantitatively obeys purely physical laws. Because it is
soluble in water and fats, some nitrogen passes through
our lungs into our circulatory system and is then
absorbed in the tissues of our body. A certain amount of
nitrogen naturally pervades our tissues at all times.
Right now, your body is saturated with dissolved nitrogen
for the surrounding air pressure. When diving, the
increased pressure of depth causes additional nitrogen to
be dissolved in our tissues. If the nitrogen loading is
excessive, it can cause nitrogen narcosis during the dive
or, if the ascent is too rapid, decompression sickness
after you surface (or in extreme cases, as you approach
the surface).
Drawbacks of nitrogen were recognized long before
the development of scuba. In 1878, French physiologist
Paul Bert established that nitrogen, liberated as bubbles
following sudden decompression, was the cause of
decompression sickness. Nitrogen bubbles collect and
Chapter 1- Introduction
expand, and the tissue or neurological insult that
results presents as signs and symptoms of the bends.
In the early twentieth century, John Scott Haldane
developed a quantitative model for nitrogen loading,
and devised tables that set safe time limits for single
dives and stage decompression schedules for dives that
exceeded the limits.
As noted above, one solution to the nitrogen problem
seems obvious–breathe less nitrogen. If the air we
normally breathe is one-fifth oxygen and four-fifths
nitrogen, why not just take out some of the nitrogen
and go diving. This is not a new idea either. Our knowledge
of the physiological effects of the gases we breathe
has grown over a long period of time, and we are still
learning.
Pure oxygen has limited applicability in diving. In
the 1870s, the same Paul Bert, in a separate set of
experiments, established that breathing pure oxygen
under pressure could cause convulsions and death.
However, the hazards were not widely known for some
time, and early scuba units were most often oxygen
Introduction
5
FIGURE 1-1: NITROX DIVING METHODS WERE FIRST PUBLISHED BY THE U.S. NAVY IN 1959 JUST AS RECREATIONAL DIVING INSTRUCTION (NAUI)
WAS ALSO DEVELOPING